JP-A-2005-308380 (corresponding to US 2005/0268644 A1) discloses an ejector refrigerant cycle device. In this ejector refrigerant cycle device, a refrigerant flow is branched at a branch portion on the downstream side of a radiator and on the upstream side of a nozzle portion of an ejector into two streams, one of which flows to the nozzle portion, and the other of which flows to a refrigerant suction port of the ejector.
In the ejector refrigerant cycle device of this document, a first evaporator is disposed on the downstream side of a diffuser portion of the ejector. Between the branch portion and the refrigerant suction port of the ejector, there are provided with a throttle mechanism serving as decompression means for decompressing the refrigerant and a second evaporator for evaporating the decompressed refrigerant to allow the evaporated refrigerant to be drawn into the refrigerant suction port of the ejector.
A pressure increasing effect of the diffuser portion of the ejector increases a refrigerant evaporation pressure (i.e., refrigerant evaporation temperature) of the first evaporator more than that of the second evaporator, so that the refrigerant can evaporate in different temperature ranges at the first and second evaporators. Furthermore, the downstream side of the first evaporator is connected to a compressor suction side, and the pressure of refrigerant to be drawn by the compressor is increased, thereby decreasing a compressor driving force and improving a cycle efficiency (i.e., performance of cycle COP).
In order to further improve the cycle efficiency, the inventors of the present application try an ejector refrigerant cycle which includes an inner heat exchanger for exchanging heat between high-temperature and high-pressure refrigerant on the downstream side of the radiator and low-temperature and low-pressure refrigerant on the suction side of the compressor in addition to the structure of the ejector refrigerant cycle device disclosed in the JP-A-2005-308380. In this case, the enthalpy of the refrigerant flowing into each of the first and second evaporators is decreased by the heat exchange of the refrigerants in the inner heat exchanger, whereby a difference in enthalpy of the refrigerant (refrigeration capacity) between the refrigerant inlet and outlet in each of the first and second evaporators is increased, thus improving the cycle efficiency as compared with the cycle disclosed in the JP-A-2005-308380.
However, when the ejector refrigerant cycle device provided with the inner heat exchanger is actually activated, the throttle mechanism on the upstream side of the second evaporator does not decompress the refrigerant sufficiently. Thus, the ejector refrigerant cycle device often operates while the refrigerant evaporation pressure of the second evaporator does not decrease enough with respect to the refrigerant evaporation pressure of the first evaporator. If the refrigerant cycle is operated in such a state, the second evaporator cannot provide a sufficient refrigeration capacity.